Patent GB-1074403-A (GB)
Title: Paramagnetic gas amalyzer
IPC: G01N27/74
Filed: 1965-04-26
Abstract: 1,074,403. Paramagnetic gas analysis. MINE SAFETY APPLIANCES ITALIANA S.p.A. April 26, 1965 [April 27, 1964], No. 17558/65. Heading G1N. In a paramagnetic gas analyzer a pair of resistor filaments A, B (Fig. 2) are disposed in an annular chamber perpendicular to the lines of maximum magnetic force therein and to the circumferential gas flow therein. The first filament A is located in a region where the product of field intensity and circumferential field intensity gradient is maximum. The filament B is located close to the first but in a region where said product is minimum. Both filaments are heated to the same temperature (e.g. 200‹C.) in the absence of paramagnetic gas. Due to the thermomagnetic effect the paramagnetic gas in a gas mixture is displaced toward regions of low magnetic intensity, and the "magnetic wind" created cools the upstream filament A and transfers heat therefrom to filament B. The difference in temperature of the filaments is proportional to the amount of gas flow and to the concentration of paramagnetic gas, e.g. oxygen, causing the flow. The resistor filaments may be connected in a bridge circuit Fig. 5 (not shown) the unbalance voltage readings of which are utilized. The bridge may be compensated for ambient temperature. There may be a plurality of magnetic fields across separate circumferential portions and a separate pair of filaments A, B associated with each as shown in Fig. 2, wherein a test cell comprises a cell body 2, polepieces 3, 4 coupled to a permanent magnet (not shown), an annular test chamber 10 the outer wall of which is formed by four polepieces extensions, 13, 14 of polepiece 3 and 15, 16 of polepiece 4. The remainder of the wall comprises brass or stainless steel inserts 18. In order to increase the temperature difference of the gas between filaments A and B recesses 19 formed in the outer wall which are lined with a strip 20 of poor thermal conductivity e.g. Teflon Registered Trade Mark. The test chamber inner wall is formed by the outer surface of a cylinder 21 which includes complementary interior polepieces 13', 14', 15', 16' of soft iron disposed opposite the outer wall polepieces, and non magnetic metal inserts 22. The annular chamber is closed on each side by a gas permeable disc 63 Fig. 1 (not shown) of sintered powdered metal and two circular end caps are clamped one on each side of the cell body each spaced from its adjacent disc to form a cap chamber. Gas flows in through pipe 40 and via each cap chamber to an outlet 44. At the same time there will be an exchange of gas, through the permeable disc, between the cap chamber and the annular test chamber 10 thus providing a continuous sampling of the mixture. The discs also have a row of circumferentially disposed holes providing passages between the test chamber and cap chambers. Alternatively Figs. 7, 8 (not shown) the filaments may be mounted radially and the magnetic fields may be parallel to the longitudinal axis of the cell. Each filament comprises a spiral of wire on a ceramic cylinder Fig.4 (not shown). The filaments A may be mounted on one end cap and the filaments B on the other whereby rotation of one or both end caps changes the spacing of and position of the filaments.